The present invention relates generally to a surface coating on a substrate on which an image is to be printed and, more specifically, to a surface coating on a substrate where the surface coating comprises a hydrophobic layer and a hydrophilic layer, wherein the hydrophilic layer is between the hydrophobic layer and the substrate.
Printed images are in common use in a variety of applications. For example, back-lighted images are often used as commercial signs, slot machine graphics, and exhibit displays. In this case, the image, typically in color, is produced on a light-transmissive substrate such as glass, Lexan.RTM., and the like. The substrate and image combination is placed in an opening of an enclosure and back-lighted by any one of a variety of light sources.
The known technique for creating the image on the light transmissive substrate is through the use of silk screening. The resulting silk screened image is comprised of a dot matrix of the inks or dyes used to create the image. The granularity of silk screened images is, however, relatively high so that it is difficult to get continuous tone, photo-realistic high color saturation and opacity with back-lighted silk screen images.
The silk screening technique also suffers from a cost disadvantage in low volume production situations. The relatively high cost of preparing the silk screens used to make the image makes using the silk screening technique impractical if only a small number of copies of the silk screen image are to be produced.
Another known technique is to use a color image produced on a light-transmissive photofilm. However, such photofilms also do not have a high opacity (3.0 density black) and color saturation when used in a back-lighted display. Moreover, the gelatin emulsion used in photofilms is subject to degradation at extended temperatures above 150 degrees Fahrenheit.
Such high temperatures are commonly experienced in back-lighted displays where heat which may not be adequately dissipated is created by the light sources of the bright light required for an effective display and from mechanical components as are used in, for example, gaming machines.
More recently, ink jet printing of colored inks onto light-transmissive media for displaying color images has become known. Such images have been widely used for overhead projection applications. While the overhead images thus produced are relatively inexpensive and are acceptable for many uses, the color saturation and opacity have been a problem. When aqueous inks are used, moreover, special coatings must be provided on the light-transmissive medium to absorb the dyes so that images of an acceptably high quality are formed. For example, U.S. Pat. No. 4,783,376 teaches coating a light-transmissive material with a polyvinyl alcohol solution before ink jet printing thereon. While the polyvinyl alcohol coating works to absorb the ink resulting in a fairly high quality image being printed, the polyvinyl alcohol coating causes individual colors of a multi-color image to bleed into each other. This bleeding results from the fact that polyvinyl alcohol is highly water soluble and tends to attract the ink in a transverse direction after the ink is applied to the coating. Yet another disadvantage of the polyvinyl alcohol coating is that the coating fails to adequately protect the dried ink from fading due to exposure to UV light.
Furthermore, to protect an image from water and UV light, it is often desirable to protect the image by overcoating same with some sort of water-repellent material. When a polyvinyl alcohol surface coating is utilized, a mineral or spirits based overcoating material must be selected. Unfortunately, this type of overcoating material presents certain environmental problems, and as a result, often presents problems with OSHA.
Finally, when printing on a medium using an ink jet method, a surface charge is typically applied to the medium. As a result, the ink jet travels in a more direct line to the medium, and a sharper image is printed. Additionally, because the surface charge causes the ink jet to be attracted to the medium, it is possible to print faster. Consequently, it is generally desirable to try to maximize the surface charge on the medium to which the image is to be printed using an ink jet. However, when a polyvinyl alcohol surface coating is utilized, the level of the surface charge must be fairly moderate else the image degrades. Another use of coated paper for ink jet printing is the application of ink to high quality fine art papers and fine art canvas for limited edition or "1-off", on demand printing of computer files. The coating layer holds the colors and offers intensities only formerly achieved through offset printing. In offset printing, multiple striking of the ink head, or various dot gain formulas are used as each paper used prints with different results. By using a coated paper of the present invention, the same ink setting can be used on all papers with the same coating, thus making the printing process more profitable, resulting in fewer setups and less testing. This particularly applies to on-demand press-direct digital offset printing.
The difficulties discussed hereinabove are substantially eliminated by the present invention.